Abstract C138: Targeting macropinocytosis in pancreatic cancer

Abstract

Abstract Pancreatic cancer is the fourth-leading cause of cancer-related deaths in the United States with a 5-year survival rate of <5%. The deadly nature of this disease compounded by a lack of effective treatment options highlights a need for new therapeutics. Past studies have suggested that pancreatic cancer cells acquire the nutrients needed for cell growth through macropinocytosis, an endocytic process by which protrusions from the cell membrane create large vesicles that transport extracellular fluid along with the constituent proteins and lipids into the cell. Additionally, several studies have suggested that macropinocytosis is regulated in part by various genes including p21 protein (Cdc42/Rac)-activated kinase1 (PAK1), ADP-ribosylation factor 6 (ARF6), and sorting nexin 5 (SNX5). In this study, we investigated the effects of knockdown of these three genes on the macropinocytic activity of pancreatic cancer cells. The goal of this study is to assess whether PAK1, ARF6, or SNX5 may serve as potential targets for the suppression of macropinocytosis in pancreatic cancer, which would hamper the cells' uptake of nutrients thus starving the cancer cells and hindering tumor growth. We carried out this study using MIA PaCa-2 pancreatic cancer cells, which are known to exhibit relatively high levels of macropinocytosis. Treatment of cells with siRNA sequences specific to the three genes resulted in a significantly decreased uptake of FITC-labeled dextran as compared to cells treated with non-targeting siRNA and cells that received no treatment, indicating that inhibiting the expression of each of the genes correlates to a reduction in macropinocytic activity. Among the three genes, PAK1 siRNAs exhibited the most significant and consistent inhibitory effect on macropinocytic activity of MIA PaCa-2 cells. We, therefore, further tested the effect of two small-molecule PAK1 inhibitors, namely IPA-3 and PF-03758309, on macropinocytosis. Treatment of cells with the inhibitors resulted in a dose-dependent decrease in the uptake of FITC-labeled dextran and FITC-labeled albumin. The inhibitors also showed potent anti-proliferative activity in pancreatic cancer cell lines. The results of this study indicate that inhibition of PAK1, ARF6, or SNX5 all resulted in reduced macropinocytic activity of pancreatic cancer cells, with PAK1 showing the most promise as a potential therapeutic target for pancreatic cancer. Citation Format: James Hunt, Serina Ng, Clifford Whatcott, Daniel D. Von Hoff, Haiyong Han. Targeting macropinocytosis in pancreatic cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C138.